1. Field of the Invention
The present invention generally relates to computer aided drafting (CAD) systems and, more particularly, to a procedure which permits the addition of dimensions to three dimensional (3D) computer models without the necessity of two models and also permits automatic documentation.
2. Description of the Prior Art
It is now possible to build solid models of parts in a general purpose computer. These models can be used to calculate properties of the parts, such as center of gravity and moments of inertia. They can also be used to test for interference between parts. Parts which are defined in a solid modeling system are not completely designed for manufacture until one adds dimensions and tolerances to the model. These dimensions and tolerances are traditionally included on the drawing of the part.
Current practice is to make projections of the solid model and send these to a two dimensional (2D) drafting system, where dimensions and tolerances are added and a complete engineering drawing is produced. The major problem with this approach is that there are two models, the 3D solid model and the 2D drawing model. When numerous changes are in progress, it is difficult to keep these two models consistent. Therefore, it would be desirable to be able to add the dimensions and tolerances to the solid model and have only one model.
Some tolerances, such as geometric forms, are parts of leaders and others are parts of dimensions on the drawing. In addition, there are usually default linear and angular tolerances in the title block of the drawing. If a dimension is shown on the drawing without a tolerance and is not declared basic or reference, then the appropriate title block tolerance applies. Since so many people are familiar with these conventions, it is desirable that a solid modeling system be consistent with them. Therefore, leaders and dimensions which can be applied to solid models are needed.